ABSTRACT
It came as a surprise when Sta ord et al. (1997) introduced the free-electron model of a nanocontact-referred to as the nanoscale free-electron model (NFEM) henceforth-and showed that this comparatively simple model, which emphasizes the quantum con nement e ects of the metallic electrons, is able to reproduce quantitatively the main features of the experimental observations. In this approach, the nanowire is understood to act as a quantum waveguide for the conduction electrons (which are responsible for both conduction and cohesion in simple metals): Each quantized mode transmitted through the contact contributes G0 to the conductance and a force of order EF/λF to the cohesion, where EF and λF are the Fermi energy and wavelength, respectively. Conductance channels act as delocalized bonds whose stretching and breaking are responsible for the observed force oscillations, thus explaining straightforwardly their correlations with the conductance steps.
